Honestly, I saw some people complaining about the "lack" of relationship and character development in this manga, and I feel that this isn't true.
While it may seem that they aren't developing a lot, the truth is that they are, only at a very slow pace. I feel that this might annoy some people, but thats the way it works in reality. You don't just meet a counselor, suddenly get over your phobias, and open up to other people. It takes time to trust and love someone, and I feel that this manga does a great job of showing that.
Another thing that I've been seing is that people are unhappy with the progression of their relationship. I'd like to point out that if you keep reading the manga, you'll learn that Shirotani isn't the only one who has emotional and mental blocks that he developed in childhood. These problems are exemplified with the way that Kurose manipulates and shuts Shirotani out completely. However, as the story progresses, it is made clear that Kurose truely loves Shirotani and genuinely is trying to help him.
Overall, this story is very slow in the developement of the characters, however it makes it much more realistic, and the later flashbacks in the manga explain and help justify the way that the two of them act. If you don't want to read something dark or slow, than please don't read this because you'll be disapointed.